130 



REPORT — 1872. 



The agreement between the first and second set of observations is remark- 

 ably close ; and as the time of leaving the thermometer in the water was 

 about half an hour in most of the observations of the first set, and two 

 hours or more in all the observations of the second set, it is obvious that 

 half an hour is a sufficient time to give a correct observation. This conclu- 

 sion is satisfactory both as regards the reliability of the observations them- 

 selves, and also as establishing the fact that this pattern of thermometer is 

 not unreasonably slow in its working. The exactness of the agreement also 

 serves to show that the thermometer can be depended on to the tenth of a 

 degree, and that we may henceforth use it with confidence. 



Before proceeding to discuss the observations, it wUl be convenient to give 

 a few particulars respecting the well, which have been kindly furnished by 

 Messrs. Mauget and Lippmann. 



It was commenced by the municipal authorities as a masonry well, by the 

 ordinary method of digging, until it had reached a depth of 34-5 metres. 

 The intention was to carry it in this way to the depth of about 135 metres, 

 the estimated depth of the tertiary strata covering the chalk ; but the diffi- 

 culties and dangers which were encountered, from the want of tenacity in 

 the soil (la nature essentleJlement ehouleuse des terrains), and latterly from 

 the insufficiency of the pumps, rendered it necessary to abandon this inten- 

 tion ; and in May 1865 the task of completing the well by boring was 

 assigned to Messrs. Degousee and Laurent, the predecessors in business of the 

 gentlemen to whom we arc indebted for these observations. A small trial 

 bore (0-2 metre in diameter) was commenced, and continued till January 1866, 

 by which time the machinery for the heavier work was ready. In order 

 to sujjport the masonry, which showed signs of giving way, it was tubed 

 through its whole length with a tube 1-8 metre in diameter and 0-02 

 metre thick, cemented externally. Erom the bottom of this tube, at the 

 depth of 34-5 metres, a bore 1*7 metre in diameter was carried to the 

 depth of 68'7 metres from the surface of the ground. A second tube 

 1'58 metre in internal diameter was inserted to the depth of 121-6 metres, 

 and a third tube of internal diameter 1'39 metre was carried down into 

 the chalky marls and the upper portion of the chalk at the depth of 

 139-15 metres from the surface. From this point downwards, the bore 

 has been driven through the chalk, and tubing has been unnecessary, its 

 diameter at the depth of 662 metres being still 1-35 metre. 



The thickness of the tertiary sLrata is 137 metres, and the elevation of 

 the surface of the ground above sea-level is 48 metres, or 157 feet. 



